1. Field of the Invention
The present invention relates to an organic light-emitting diode (OLED) device, and more particularly to an organic light-emitting diode device with efficiency roll-up property.
2. Description of the Prior Art
An organic light emitting diode (OLED) was invented by C. W. Tang and S. A. VanSlyk et al. of Eastman Kodak Company in 1987 and manufactured by a vacuum evaporation method. A hole transporting material and an electron transporting material (such as Alq3) are respectively deposited on a transparent indium tin oxide (abbreviated as ITO) glass, and then a metal electrode is vapor-deposited thereon to form the self-luminescent OLED apparatus. Due to high brightness, fast response speed, light weight, compactness, true color, no difference in viewing angles, no need of liquid crystal display (LCD) type backlight plates as well as a saving in light sources and low power consumption, it has become a new generation display.
In addition to light-emitting material layers, the conventional OLED device is often added to other intermediate layers, such as an electron transport layer and a hole transport layer, so as to enhance the efficiency of the OLED device. Referring to FIG. 1, which is a structural drawing of a conventional OLED device. As shown in FIG. 1, the conventional OLED device 1′ includes a cathode 11′, an electron injection layer 12′, an electron transport layer 13′, a first light-emitting material layer 14′, a second light-emitting material layer 15′, a hole transport layer 16′, a hole injection layer 17′, and an anode 18′.
The above-mentioned conventional OLED device 1′ is an OLED device with high efficiency. However, referring to FIG. 2, which is a curve diagram of the luminous efficiency of the conventional OLED device 1′. As shown in FIG. 2, when the brightness of the conventional OLED device 1′ is higher than 3500 cd/m2, the luminous efficiency of the conventional OLED device 1′ is decreased rapidly. Such a phenomenon is called an Efficiency Roll-Off phenomenon of the conventional OLED device 1′.
According to the conventional OLED device has the drawback of the Efficiency Roll-Off, OLED manufacturers have made great efforts to make inventive research thereon and eventually provided an OLED device with mixed light-emitting layer. Please refer to FIG. 3, which illustrates a structural drawing of an OLED device with a mixed light-emitting layer. As shown in FIG. 3, the OLED device 1″ with the mixed light-emitting layer includes: a first conductive layer 11″, a hole injection layer 12″, a hole transportation layer 13″. A first light-emitting layer 14″, a second light-emitting layer 15″, an electron transportation layer 16″, an electron injection layer 17″, a second conductive layer 18″, and a third light-emitting layer 19″, wherein the first conductive layer 11″ is an Indium Tin Oxid (ITO), used as an anode of the OLED device 1″. The hole injection layer 12″, the hole transportation layer 13″, the first light-emitting layer 14″, the third light-emitting layer 19″, the second light-emitting layer 15″, the electron transportation layer 16″, the electron injection layer 17″, and the second conductive layer 18″ are sequentially formed on the ITO substrate.
In the aforesaid OLED device 1″ with the mixed light-emitting layer, the the third light-emitting layer 19″ is formed by mixing part of the first light-emitting layer 14″ and part of the second light-emitting layer 15″, and the thickness of the third light-emitting layer 19″ should be less than 10 nm. Please refer to FIG. 4, which illustrates a curve diagram of the luminous efficiency of the OLED device with the mixed light-emitting layer. As shown in FIG. 4, the solid curve with solid triangles represents the luminous efficiency data plot of the prior art OLED device; the dashed curve with hollow circles represents the luminous efficiency data plot of the OLED device 1″ with the mixed light-emitting layer. Wherein when the brightness of the OLED devices exceed 3500 cd/m2, the solid curve and the dashed curve begin to decline. However, when the brightness is about 10000 cd/m2, the hollow circles on the dashed curve are higher than the solid triangles on the solid curve. Thus, through the curves shown in FIG. 4, it can understand that the Efficiency Roll-off phenomenon in the high-brightness area of the OLED device 1″ with the mixed light-emitting layer is improved greatly compared to the prior art OLED device.
Accordingly, through above descriptions, it is able to know that the OLED device with the mixed light-emitting layer may improved the drawback of the efficiency roll-off existing in the prior art OLED devices. However, the brightness and the luminous efficiency showed by the OLED device with the mixed light-emitting layer are still inadequate for making the OLED devices with the mixed light-emitting layer to replace the LED devices being used as the lighting devices and display devices.
Thus, in view of the conventional OLED device and the OLED devices with the mixed light-emitting layer still have shortcomings and drawbacks, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided an organic light-emitting diode device with efficiency roll-up property.